Summer 2011

Know How

Soil quality may be thought of as a three-legged stool. It’s balanced when each leg – soil structure, organic matter and soil life – works with the others to create a healthy system supporting plant growth.

STRUCTURE improves soil as a medium for plant growth and provides the habitat for biological activity. The gluing together of sand, silt and clay particles creates a range of pore sizes. Larger pores facilitate gas exchange and drainage and allow easier root growth. Smaller pores store water and protect microbes, the smallest members of the biological community.

ORGANIC MATTER is the fuel driving the system. The biological community decomposes plant residue and animal waste, releasing nutrients in plant available forms. Waste glues primary soil particles together, improving structure.

SOIL LIFE is the key to the system. Bacteria and fungi cycle nutrients and improve structure. Earthworms and night crawlers redistribute organic matter and concentrate nutrients while creating “biopores” that improve gas exchange, drainage and root growth.

1 Minimize tillage. Tillage destroys structure and biological habitat. It disrupts biopores and the communities that produce them, resulting in population declines. Tillage also harms mycorrhizal fungi whose intimate association with plants improves water and nutrient uptake and whose waste product, glomalin, is a biological “super glue” that binds soil particles together in a waterproof manner.

2 Keep the surface covered. Raindrop impact has a devastating effect on structure at the soil surface. Clay particles become detached and fill pore spaces, creating a crust. This reduces gas exchange and water infiltration, inhibiting subsurface biological activity—including root growth—and promotes soil erosion and nutrient run-off on slopes. Conservation tillage (which leaves more crop residue), mulching and cover crops all protect the surface in the absence of a crop canopy.

3 Manage traffic. The physical force of traffic, whether large equipment in a field or walking between rows in the garden, can destroy structure by the process of compaction. Compaction reduces total pore space and harms the habitat of soil life.

4 Add organic matter. Returning organic matter to the soil in the form of compost or manure adds nutrients, stimulates biological activity and can improve tight soils by acting as a bulking agent, increasing pore space.

5 Use cover crops. These unharvested crops are grown to protect soil, and often their green tissues are returned to the soil. This addition of fresh, readily decomposable organic material will stimulate a pulse of biological activity and the soil quality benefits that come from it. Many legume species—red or berseem clover, for example—will promote mycorrhizal abundance and glomalin production.

Contributed by Jim Stute, educator, UW Extension Rock County

This article was posted in Know How, Summer 2011, Uncategorized.